(1) Field of the Invention
This invention generally relates to trajectory control and more specifically to a method and apparatus for providing guidance parameters at launch that direct a pursuing vehicle from a launching vehicle to a target vehicle capable of evasive maneuvering after the target vehicle becomes alerted to the presence of the pursuing vehicle.
(2) Description of the Prior Art
The trajectory control of a pursuing vehicle can be classified as post-launch or pre-launch control. In post-launch control, guidance information is sent from the launching vehicle to guide the pursuing vehicle to the target vehicle. The following U.S. Letters Patent disclose such post-launch trajectory control systems:
______________________________________ 3,260,478 (1966) Welti 3,643,616 (1972) Jones 3,784,800 (1974) Willoteaux 5,319,556 (1994) Bessacini ______________________________________
The Welti patent discloses the control of a first object in dependence upon a position of a second object for collision or anti-collision purposes. A regulator, that controls the travel and includes a travel control member for the first object, receives positional information of the first and second objects as a pilot magnitude and a reference magnitude. One of the positional informations is delayed in dependence upon a timing interval proportional to the time change of the quotient of the distance information of the two objects. The regulator subsequently supplies an output magnitude to the travel control member that represents the time differentials between the angular co-ordinates of the first and second objects modified by a disturbance magnitude.
The Jones patent discloses a method and apparatus for guiding a torpedo along a collision course to a moving target ship. A control system on the launching vehicle sends guidance parameters over a communication cable to maintain a predetermined, substantially constant lead angle with respect to the target ship by adjusting torpedo speed as the torpedo travels toward an anticipated collision.
In the Willoteaux patent a trajectory control system calculates the distance between a moving body and other moving or stationary objects by taking account of the speeds and direction of each. The control system simulates a series of hypothetical trajectories diverging on either side of the actual trajectory until a hypothetical trajectory is determined which satisfies various imperatives. The system then instructs the moving body control system to change the linear and or angular speed thereof so that the moving body follows the latter trajectory.
The Bessacini patent discloses an adaptive trajectory apparatus and method for providing, after launch, vehicle control commands to steer an underwater vehicle launch from a vessel toward a contact. As commands produced by this system transfer by between the launching vessel and the launched vehicle over a communications link.
As generally found in prior art post-launch control systems, a pursuing vehicle exits a launching vehicle. Control systems on the launching vehicle monitor the relative positions of the pursuing vehicle and a target vehicle or contact and control the pursuing vehicle by the transfer of information between the launching vehicle and the pursuing vehicle over a communications link. When the launching vehicle is a submarine and the pursuing vehicle is a torpedo, the communications link typically comprises a communications wire. If the pursuing vehicle is a missile the communications typically occurs over some radio link. In either case, post-launch control systems on the launching vehicle issue guidance parameters to guide the pursuing vehicle along some trajectory into a predetermined relationship with the target vehicle.
In a pre-launch system, the pursuing vehicle follows a predetermined trajectory after launch that may or may not be programmable prior to launch. However, with either type, the pursuing vehicle leaves the launching vehicle and travels along a trajectory that may be simple or complicated. With torpedoes, missiles and the like that may undergo pre-programmed maneuvers, the input guidance parameters may include gyro angles and time lapses, including, for example, the time lapse between the launch and the enablement of any instrumentation on the pursuing vehicle, such as an acoustic seeker on a torpedo.
In order to provide the most accurate pre-launch guidance parameters to the pursuing vehicle, it is necessary that the interval between the time a last estimate of target vehicle state is made and the time a pursuing vehicle is launched be quite short. It is during this interval that a prior art pre-launch system must produce the guidance parameters, and this interval has constrained the nature of the analysis required to produce such guidance parameters. For example, prior art pre-launch systems generally assume that the target will maintain a constant velocity even after the target becomes alerted to the presence of the pursuing vehicle. In actual practice, however, a target normally takes evasive action by turning, changing speed or both. Some prior art pre-launch systems take such actions into account by launching two or more pursuing vehicles along the calculated course and one or more offset courses.
The above-identified Bessacini et al. patent application Ser. No. 08/521,207 discloses a method and apparatus that overcome many of the foregoing problems and deficiencies. This method and apparatus provide pre-launch guidance parameters within a short time interval and take evasive action of a target vehicle into account. Models of the pursuing vehicle and target vehicle provide proposed trajectories based upon various environmental considerations and possible evasive tactics. A guidance system uses estimates of initial operating parameter solutions, such as gyro angle, alertment time and intercept time, to begin a convergent, iterative process that defines final operating parameter solutions from which the guidance parameters are determined and transferred to the pursuing vehicle at launch.
In accordance with the disclosed method and apparatus, an operator enters an evasive action as an initial parameter that can be independent of the tactical situation facing the target vehicle. That is, the selection of a particular evasive action is somewhat arbitrary or subjective because the selection is primarily dependent on the experience of an operator at the launching vehicle. While the operator may guess the general nature of an evasive action, the operator determines the evasive action without knowledge, for example, of the actual bearing from the target vehicle to the pursuing vehicle at alertment. However, in general, the target vehicle will base an actual evasive action upon that bearing. The evasive actions that the operator guesses and the target vehicle takes may be the same in general terms; for example, a turn of 90.degree.. However, the actual courses will differ if the base line for the operator's guess is not the bearing on which the actual evasive action is based. Moreover, in some situations, bearing from the target vehicle to the pursuing vehicle might actually dictate an entirely different evasive action from that selected by the operator on the launching vehicle even though only a small difference exists in the situation perceived by the operator in advance and at the target vehicle at alertment.